1993 AHSME Problem 10

Let r be the number that results when both the base and the exponent of a^b are tripled, where a,b>0. If r equals the product of a^b and x^b where x>0, then x=

\text{(A) } 3\quad \text{(B) } 3a^2\quad \text{(C) } 27a^2\quad \text{(D) } 2a^{3b}\quad \text{(E) } 3a^{2b}

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.